Real Clear Polittics reports that despite his questionable allegations, Obama's negative ad blitz apparently did not gain him an edge. He remains at 50/50 vs. Romney, whose preferences and favorables have been rising.
Obama massively outspent Romney in June, largely because Romney's campaign can't spend mney until he is formally nominated. Nevertheless, Romney remains in a statistical tie with Obama. That's a frightening concern for an incumbent.
Not all polls are equally valid due to the different samples. Some sample Registered Voters. Some sample Likely Voters. And and party distributions in the sample are subject error based on pollers bias and changing party preferences.
Expect to see Romney's favorables rise and Obama's continue to fall as Republican spending kicks in and hammers Obama for the bad economy and his false promises.